Mammals’ Tooth Characteristics Evolved on Two Continents

The specialized teeth that enabled ancient, shrew-like creatures to flourish and gave rise to all modern mammals evolved independently in two animal groups living continents apart, researchers from the Carnegie Museum of Natural History report in today’s Nature. The finding could dramatically alter theories about the pace of early mammals’ global advance in the waning days of the dinosaurs, more than 65 million years ago.

By comparing characteristics of teeth from mammals that lived between 65 million and 200 million years ago, the researchers concluded that the advanced molars, called tribosphenic molars--that ensured the small creatures’ success by allowing them to eat a wider range of foods--evolved in two mammal groups that arose separately on northern and southern continents, rather than just once, as had previously been believed.

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--Compiled by Times medical writer Thomas H. Maugh II